Nova Launcher is the go-to launcher for so many not just for the sheer amount of customization it offers, but also the speed and frequency at which the team instills new features. However, one feature that people have constantly clamored for has always been left out: Google Now integration. It just couldn't be added due to constraints that Google had put in place. But today, Nova Launcher is finally receiving this long-awaited functionality.
The Google app used to grant apps permission use the Now pane if it was a system app. When the Xperia Home launcher added Now functionality, enthusiasts begged for their favorite third-party launchers to include it (see the comments here). Nothing could be done, though, as an app can't be moved to the /system partition without root access. The Google app would also allow for the Now pane to be displayed if the Google app itself was debuggable, but that was a situation that was virtually never encountered.
However, the Google app's check was changed a few updates back. Because the Google app now checks if the client app is debuggable and not the Google app itself, third-party apps such as Nova Launcher can now utilize the API so long as the client is debuggable. But because debuggable apps have multiple issues (not publishable on the Play Store, some ART optimizations get disabled, and security can be weaker), a workaround had to be created.
With Nova, an appropriately-named companion app called 'Nova Google Companion' will be utilized to add Google Now functionality. This app fulfills the Google app's necessity for the client to be debuggable, but since it's debuggable, it can't be published on the Play Store. So if you want the Now pane, you'll have to download this companion from APK Mirror. Starting from Nova Launcher 5.3-beta1 (which can be downloaded from APK Mirror here, if the launcher detects the companion APK (get it from APK Mirror here), the Now pane will be activated. This will work on any device running Android 6.0 Marshmallow or higher. Nova Launcher Prime is not necessary to use this.
Now, it's worth noting that this still isn't perfect. I ran into a few issues where the launcher wouldn't detect the Google API, and thus, not allow the Now pane to be opened on my Galaxy S8+, but you have to remember that this is still a brand new feature. Over time, these kinks will get fixed, and the experience will be seamless.
If you want some of that sweet Google Now integration on your device, you can download the APK from APK Mirror. Nova Launcher 5.3-beta1 and higher will activate the Now pane if this companion app is detected. This will work on any device running Android 6.0 Marshmallow or higher, and Nova Launcher Prime is not necessary. (But seriously, Nova Prime is worth the $4.99.)
Version 5.3 of Nova Launcher is now in the stable release so you no longer need to be part of the beta. However, you still need the Nova Google Companion app to be able to see the Google Now/Feed integration on the homescreen.